Apparatus for controlling the temperature of metal lances in molten baths



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APPARATUS FOR CONTROLLING THE TEMPERATURE OF METAL LANCES IN MOLTENBATES Filed March 31. 1967 4 Sheets-Sheet l m N J l (D w u.

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APPARATUS FOR CONTROLLING THE TEMPERATURE OF METAL LANCES IN MOL'TENBATHS Filed March 31, 1967 4 Sheets--Sheet 2 July 28, 1970 N. J.THEMELIS APPARATUS FOR CONTROLLING THE TEMPERATURE OF METAL Filed March31, 1967 LANCES IN MOLTEN BATHS FIG.4

4 Sheets--Sheet 3 July 28, 1970 N. J. THEMELIS 3,521,872

APPARATUS FOR CONTROLLING THE TEMPERATURE OF METAL LANGES IN MOL-TENBATHS Filed March 31, 1967 4 Sheets-Sheet 4 United States Patent3,521,872 APPARATUS FOR CONTROLLING THE TEMPERA- TURE 0F METAL LAN CESIN MOLTEN BATHS Nickolas J. Themelis, Beaconsfield, Quebec, Canada, as-

siguor to Noranda Mines Limited, Toronto, Ontario, Canada Filed Mar. 31,1967, Ser. No. 627,466 Claims priority, application Great Britain, Apr.13, 1966, 16,232/ 66 Int. Cl. C21c 7/00 US. Cl. 26634 10 Claims ABSTRACTOF THE DISCLOSURE A water-cooled lance which may be used in thetreatment of molten metal and which may be inserted beneath the surfaceof the metal. The lance structure provides a passage for gases and apassage for a coolant such as Water. The water vaporizes as it contactsthe hot lance body and so acts as a cooling medium and the gas and watervapour are admixed as they pass through the lance body and enter themolten metal as a gaseous mixture.

This invention relates generally to a method and apparatus forcontrolling the temperature of metal lances in molten baths.

The major problem in introducing gases in molten metal baths forpurposes of refining or converting has been that irrespective of theflow of gas through the lance, the heat transfer from the bath to thelance greatly exceeds the possible heat transfer from the lance to thegas stream within it. As an example, a steel lance exposed to a furnaceatmosphere of 2400 F. may absorb a maximum heat input of 100,000B.t.u./hr.ft. of exposed surface. The same lance, when submerged in abath of molten copper at 2200 F., absorbs an estimated 400,000 to800,000 B.t.u./hr.ft.

This enormous heat transfer rate in the molten bath is due to the factthat the conductivity of the liquid material is extremely high and alsoto the fact that the bath is usually superheated to at least 100 to 200F. above its melting point and, therefore, constitutes a practicallyinfinite source of heat due to the strong convection currents existingin the bath. On the other hand, for convection between the lance walland the gas stream flowing through the lance at sonic, or evensuper-sonic gas velocities, the maximum heat transfer rates that can beachieved are in the order of 30,000 to 60,000 B.t.u./hr.ft. It can,therefore, be seen that it is almost impossible to prevent the lancewall from reaching the temperature of the bath even at the highestpossible flow rate of gas through it, due to the limitation of the heattransfer coefficient by convection between the wall and the gas.Consequently, soon after the lance has been introduced into the bath, itreaches the temperature of the latter and because of the strongvibration caused by the gas injected in the bath, the lance is very soonbroken up.

This problem has appeared to be insurmountable, since when used with agas flow alone, even the best qualities of stainless steels and alloylances available have very little strength in the temperature of moltencopper baths and none at all in molten steel. The way in which thisobstacle has been overcome in steel refining by the new oxygen lancetechnique for steel refining, is to avoid immersing the lance into thebath and also to provide the lance with a water-cooled jacket. However,in order for this method of injection to be effective, it is requiredthat the oxygen emerges from the lance at very high velocities and alsothat the lance is kept at a safe distance above the bath; these factorshave a pronounced effect on the efficiency utilization of oxygen gas.

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In the case of copper processing where the gas must be introduced belowthe surface, the use of lances has met with complete failure and hasprevented the adoption of gas injection techniques into stationaryfurnaces not equipped with refractory tuyeres. In particular, failure ofthe lances has prevented their use in the deoxidation of anode copper.

The present invention relates to an eifective method for overcoming thisproblem and allowing the use of, for example, mild steel or other metalpipes for injecting gases in molten baths.

The lance of the present invention may be used generally for introducinggases into molten metal at-high tempertaures. In a process ofdeoxidizing copper by hydrocarbon gases, steam and hydrocarbon gases,such as propane and butane, may be mixed and reacted in the lance of thepresent invention. The steam may be replaced by water which is bothvaporized and reacted in the same lance. The benefit of mixing waterinstead of steam is that the lance can be kept cooler making it possibleto use ordinary mild steel pipes for introducing various gases intomolten metals at high temperatures.

Advantages of the invention over previous water-cooled lances, such aswater-cooled sheathed lances or the lance disclosed in US. Pat. No.3,269,829 include the presence of a very advantageous safety aspect.Since the cooling water is atomized at a location outside the bath therecan be no danger of structural failure of the lance or accidentaldischarge of a volume of water sufficient to cause an explosion incontact with the molten bath. Therefore, the tip of the present lancecan be immersed in the liquid bath, since a failure of the tip will notafiect the formation of the fine water spray. All other types ofwater-cooled lances referred to above cannot be immersed in the liquidand must be kept at a safe distance above the bath.

In the drawings:

FIG. 1 is a side elevation of a rotary anode furnace with a cut-awaysection showing a lance of the present invention disposed therein.

FIG. 2 is a side view of a reverberatory anode furnace showing threelances in position in openings of the furnace.

FIG. 3 is a cross-section showing the atomizing nozzle of the lance ofthe present invention.

FIG. 4 is a section of a reverberatory furnace with a lance extendingthrough a side port thereof into the melt.

FIG. 5 is a cut-away section of the lance showing the flow of water-gasmixture therein.

Broadly speaking the invention relates to a method and apparatus forcontrolling the temperature of pipes or other lancing devices, used forinjecting a gas into a molten bath, by introducing a finely dividedspray of water into the gas stream thereby greatly enhancing the heattransfer rate between the wall of the lancing device and the gas stream,and maintaining the lance at a temperature below the temperature of thebath, thus preventing fracture or dissolution of the lance material.This method and apparatus may be used in copper refining, either for theoxidation of blister copper or for reducing with gaseous reagents,converting of copper, refining of steel by oxidation or other means, andany other process or scheme where it is necessary to inject a gas streaminto a molten bath of metal, matte, or slag.

The invention is based on the consideration that the heat transfercoefficient between the wall and the gas stream must be increasedconsiderably in order to remove the heat received by the outside wall ofthe lance. This is achieved by introducing a very fine spray of water inthe gas stream at the inlet of the lance located outside the furnace.The size of the spray droplets is preferably less than microns. Apneumatic nozzle is used which disperses a relatively low flow of waterfor example (30 gal/hr.) into the gas stream in the form of very finedroplets which, when they collide with the wall of the lance, absorb alarge amount of heat by evaporation and then are reflected back into themain stream, much in the same way as a Water droplet falling on a hotplate and bouncing on it until it is completely evaporated. The waterflow rate required will depend on the characteristics of heat transferfrom the liquid bath to the lance (temperature of the bath, lancediameter, thermal conductivity, viscosity, specific heat and density ofthe liquid bath).

In this way, the heat transfer between the gas stream and the lance isincreased enormously since the heat transfer coeflicient is not any moreone between gas and wall, but between droplet and wall, which haspractically infinite capacity as a heat sink.

FIG. 1 shows a typical rotary furnace A as used in copper refining. Thistype of furnace is supported on rollers 21 and may be rotated by asuitable motor connected to a ring gear 22. Steam is brought to thefurnace via a pipe 1 and is controlled by a pressure regulator 2 whichkeeps the steam in a loader pipe 4 at a constant pressure. Steam feed toeach lance is controlled by individual valves 3 and is connected to thelance with a flexible hose 5. A hydrocarbon, such as propane or butane,is brought to the furnace via pipe '7 and controlled by a main valve 8.The feed to each lance from a common loader pipe is also controlled byindividual valves 9 and connected to the lance by flexible hose 11. Thelance assembly consists of a mixing T 6 into which the steam andhydrocarbon is introduced, lance hanger 15, lance bushing 12 and lance14. The lance slip-bushing 12 allows the lance to be manually ormechanically rotated periodically through. 180 about the lance axis inorder to compensate for upward bending of the lance tip. The lancehanger is designed to suspend the lance at the proper angle for maximumdepth of lance orifice 17 under the melt surface 19. The whole assemblyis suspended to a suitable support by a hook 16 and cable or rope 24.

The lances in FIG. 1 are shown introduced through openings 18 in the endwalls 13 of the furnace. However, it is also understood that the lancemay be introduced through any openings in the furnace that are foundsuitable, such as openings around the cylindrical shell of the furnace23.

FIG. 5 is a section of the lance of the present invention as it isintroduced into a metal melt 20. Water or other liquid such as naphthais delivered through an inlet tube 34 and end adapter 35 to a mixing andatomizing nozzle 36 and into the lance 14 through an orifice 37. The gasto be introduced into the molten metal is delivered to the lance 14through an opening 33 in a mixing T 6 and passes through the atomizingand mixing nozzle 36 into the lance .14 through orifice 38. The orifices38 are so shaped and dimensioned that water enters the lance 14 in theform of a fine spray. As the mixture of water droplets and gases passthrough the lance 14, in the process of copper deoxidation, the Water isvaporized and reacts with the hydrocarbon gases in the lower hot sectionof the lance. It should be understood that gases other than hydrocarbonsmay be used when the purpose of adding water is solely to cool thelance. It should also be understood that the method used for the lanceis only applicable when water is not detrimental to the particularprocess for which the lance is used. The resulting gases or gas-steammixtures enter the molten metal through lance orifice 17 and risethrough the melt 20 to the liquid metal surface 19 in the form ofbubbles. Treatment of the melt 20 may consist of either a reactionbetween one, some, or all of the gases entering the melt and someimpurity of the metal itself, such as in the removal of oxygen frommolten copper, or the gases introduced may only act to remove otherdissolved gases in the melt such as in common degassing processes.

The present lance has been tested in the gaseous atmosphere of an anodefurnace at temperatures of about 2300 F., when a water flow rate of fivegallons per hour was found sufficient to maintain the pipe below 1800 F.at its tip; the corresponding gas flow rate was 30 s.c.f.m. (standardcubic feet per minute) of propane. The lance was also tested under theextreme conditions prevailing when the lance is immersed to a distanceof approximately four feet in a bath of molten copper when the requiredwater flow rate was about 20 gal./ hr. for the same gas flow rate of 30s.c.f.m. of propane.

It should be noted that the present method of cooling the lance byintroducing a finely atomized spray of water affords great flexibilityin controlling that part of the lance which in operation is submerged inthe furnace melt since it is possible, by introducing more or lesswater, to increase or decrease the temperature at the tip of the lanceas desired.

At the same time, since the metal of the lance can be kept at arelatively low and safe temperature, this invention dispenses with thenecessity of using expensive or extremely strong stainless steels forlancing applications. In the example discussed previously herein, a mildsteel pipe was introduced at an angle into the molten copper to a depthof two feet (corresponding length about four feet) and was subjected tointense conditions of vibration by introducing an overall gas rate ofs.c.f.m. which resulted in very intense mixing conditions in the bathand vibration of the lance. Yet, two hours after the lance wasintroduced in the furnace, it was still operating at the same depthwithout showing any adverse effects of attack by the liquid bath orfatigue fracture.

It is clearly apparent from the foregoing that the lance of the presentinvention represents a significant advance in the art.

I claim:

1. A lance suitable for use under high temperature conditions in thetreatment of molten material which comprises:

(a) a feed chamber adapted to allow the flow of a gaseous treatingmedium therethrough;

(b) a gas inlet in one wall of the feed chamber;

(c) a coolant liquid transmitting conduit extending axially through saidchamber and terminating in a liquid outlet in a second wall of the feedchamber;

(d) at least one gas outlet in said second wall angled and positionedsuch that the flow of gaseous treating medium therethrough causescoolant liquid flowing through the liquid outlet of the transmittingconduit to disperse into liquid droplets; and

(e) an elongated body defining a flow passage extending axially throughsaid body, said passage being adapted to receive the mixture of liquiddroplets and gaseous treating medium and having one end terminating atthe second wall of the said chamber and a second end terminating in adischarge outlet, said elongated body being adapted to be at leastpartially submerged in molten material and to be cooled internally bythe impingement of liquid droplets on the walls of the flow passage.

2. A lance as claimed in claim 1 wherein the feed chamber issubstantially T-shaped.

3. A lance as claimed in claim 2 wherein the gas inlet is situated inthe base of the T-shaped chamber which is adapted for connection to asource of gaseous treating medium and the coolant liquid transmittingconduit traverses in the horizontal portion of the T-shaped chamber andis formed as a single unit with said second Wall.

4. A lance as claimed in claim 2, wherein said feed chamber is adaptedfor detachable connection to said body.

5. A lance as claimed in claim 1, wherein said feed chamber is adaptedfor detachable connection to said body.

6. A lance as claimed in claim 1 wherein said'coolant liquidtransmitting conduit and said second wall are formed as a single unit,the end of said conduit remote from said second wall being adapted forconnection to a supply source of coolant liquid, the other of saidconduit terminating in the liquid outlet at said second wall.

7. Apparatus for use under high temperature conditions in the treatmentof molten material which comprises a lance having:

(a) a feed chamber adapted to allow the flow of a gaseous treatingmedium therethrough;

(b) a gas inlet in one wall of the feed chamber;

() a coolant liquid transmitting conduit extending axially through saidchamber and terminating in a liquid outlet in a second wall of the feedchamber;

(d) at least one gas Outlet in said second wall angled and positionedsuch that the flow of gaseous treating medium therethrough causescoolant liquid flowing through the liquid outlet of the transmittingconduit to disperse into liquid droplets;

(e) an elongated body defining a flow passage extending axially throughsaid body, said passage being adapted to receive the mixture of liquiddroplets and gaseous treating medium and having one end terminating atthe second wall of the said chamber and a second end terminating in adischarge outlet, said elongated body being adapted to be at leastpartially submerged in molten material and to be cooled internally bythe impingement of liquid droplets on the walls of the fiow passage; and

(f) a first source of supply of a gaseous treating medium, a secondsource of supply of a coolant liquid, a first conduit member connectingsaid first source of supply to said gas inlet into the feed chamber, a

second conduit member connecting said second source of supply to saidcoolant liquid transmitting conduit and adjustable valves adapted tocontrol the flow of gaseous treating medium and coolant liquid from saidfirst and second sources respectively.

8. The apparatus as claimed in claim 7 including supporting mechanismfor suspending the lance body in operating position.

9. The apparatus as claimed in claim 7 including means connected to saidlance permitting its rotation through an angle of about the lance axis.

10. The apparatus as claimed in claim 9 wherein said means on said lanceis a slip bushing.

References Cited UNITED STATES PATENTS Re. 26,36 4 7/ 1965 Kurzinski.2,937,864 5/ 1960 Kesterton. 3,093,157 6/1963 Aitken et al. 239-4245 X3,093,314 6/19-63 Meyer 239425 X 3,291,471 12/1966 Heyer.

FOREIGN PATENTS 841,350 7/1960 Great Britain.

1. SPENCER OVERHOLSER, Primary Examiner I. S. BROWN, Assistant ExaminerUS. Cl. X.R. 239425

